Hi jambandbrian.
Go to
System Preferences > Network > Show: Network Port Configurations, and make sure that the configuration used to connect to Internet appears at the top of the list.
Mail Help has some articles devoted to sending problems, e.g.
"I can't send email" or
"I can't send email because the connection to the server on port 25 timed out". You may want to take a look at them in case there is something there that applies to you. Something that usually works is changing the outgoing server port to 587 instead of 25.
That said, .Mac is having problems lately (again). This time the problem seems to be the outgoing server. I don't know what the problem will be next week. Don't be surprised if the problem fixes itself after some time for no apparent reason. You may want to report it to
.Mac email support.